The instant invention relates to a laser focussing means and especially concerns an automatic displacement mechanism for translational motion of a lens in a laser focussing optical system.
Lasers frequently are used for scanning or machining of work-pieces. That requires the laser beam to be focussed at various points on a surface of a workpiece to be operated on. A corresponding arrangement is illustrated diagrammatically in FIG. 1. A laser beam emitted by a laser 1, first, is widened by a lens system 2, 3 in order then to be focussed again. The focussed laser beam is directed by two movable mirrors 4, 5 onto a working surface 6. The focal length of the lens system 2, 3 is designed so that the laser beam will be focussed at a desired point on the working surface 6. By varying the angle of adjustment of the mirrors 4 and 5, the laser beam can be directed at different points on the working surface 6. That, however, inherently changes the length of the optical path between the lens system 2, 3 and the incident point of the laser beam on the working surface 6. For the laser beam to become focussed again on the working surface, the focal length of the lens system 2, 3 must be adjusted accordingly. That is achieved by shifting a lens 2 along the optical axis of the laser system.
It is known in the art to accomplish such displacement of the lens 2, for instance, by linear motors or a galvanometer scanner whose rotational movement is converted into linear movement by means of a flat band spring arrangement.
However, because of the nature of the adjusting mechanism, these means of dislocating the lens are rather slow and, therefore, not useful for the faster scanning speeds which adjustable mirrors would allow easily. Moreover, it would be desirable to know the precise position of the displaceable lens. That, however, cannot be determined by the known systems, or at least not satisfactorily.